The presence of hydrogen sulfide in gas streams causes different problems in oil, gas and petrochemical industries and even wood and drink industries. Removing H2S from gas streams has, hence, changed to a necessary process. Furthermore, the regulations of environment conservation organizations, on the permitted amounts of H2S are getting more and more strict every day. This is mainly because of the poisonous and corrosive effects of H2S.
Application of an aqueous solution of a polyvalent metal chelate catalyst for the oxidative removing of H2S, from gas streams and its conversion to elemental sulfur has been well known. In these processes, H2S-containing gas is contacted with an aqueous solution of a polyvalent metal chelate in a contact zone. The contactor can be any suitable device for gas—liquid contact, such as an absorber, a static mixer, a venturi scrubber, or even a combination of all. The aqueous catalyst solution absorbs H2S and converts it to elemental sulfur rapidly. As a result of this the higher oxidation state of the ion is reduced to its lower state. The lower oxidation state of the ion metal is then oxidized, as a result of contact with an oxygen containing gas to its higher oxidation state and is returned to the contact zone. Such reactions are called liquid Redox reactions. The separation of the solid particles can take place either before or after regenerating of the polyvalent metal chelate.
Due to settling or sedimentation of sulfur particles, however, the contactor can become plugged. If the settling happens to a great extent and the tower is plugged, this will perturb the contactor, in particular an absorber, and it will ultimately flood. In the case of the application of an absorber, filled with a packing, the choice of the packing material is also important. Usually a suitable packing has to be selected, which results in the least setting of solid sulfur particles. Often, such a packing does not exhibit optimum reaction rates.
U.S. Pat. No. 4,784,754 discloses a process for removing sulfur particles from an aqueous polyvalent metal ion or polyvalent metal chelate solution by a method of sinking the sulfur particles (gravity sedimentation) in a zone. In order to reduce foam and/or froth floating on a surface of the zone, sulfur particles suspended as a froth or foam are agitated and removed in a plurality of streams including at least one stream at a short distance from the top of the solution in the zone and at least one stream from the bottom of the solution in the zone. Subsequently, the streams are recombined for further processing.
U.S. Pat. No. 4,816,238 discloses another process for the removal of hydrogen sulfide from a sour gaseous stream, wherein an aqueous alkaline solution is contacted with a polyvalent metal chelate in a higher valence state in order to oxidize the hydrogen sulfide or sulfide present to sulfur. Particular measures for preventing clogging of sulfur particles in the oxidizer are not disclosed.
EP 0 582 337 A discloses another process for removing hydrogen sulfide from a gas mixture. U.S. Pat. No. 5,122,351 discloses another process for removing hydrogen sulfide from a process gas, wherein a closed loop evaporator/condenser process is interposed in the sulfur washing/filtering/recovery process in order to recover and re-use a catalytic polyvalent metal redox solution. Wash water used to purify the sulfur and any polyvalent metal redox solution recovered from a sulfur melter are fed to an evaporator to concentrate the redox solution to a concentration capable of effective absorption of hydrogen sulfide. Furthermore, the water evaporated in the evaporator is condensed as pure water for use in washing and/or filtering the recovered sulfur. Particular measures for preventing clogging of sulfur particles in the oxidizer are not disclosed.
EP 0 186 235 A1 discloses a process for removal of acid gases from a sour gaseous stream. In the process a sour gaseous stream comprising H2S is contacted in a column with an aqueous reactant solution comprising an effective amount of Fe(III) chelate of an organic acid to obtain a sweet gaseous stream and a mixture including solid sulfur and Fe(II) chelate of the acid. Degradation of the iron chelate in the reactant solution employed in the cyclic process is inhibited by maintaining a relatively high Fe(II) chelate concentration by carrying out the regeneration step in the column as a plug flow contracting procedure. The problem of foaming and flooding of the oxidizer is not discussed specifically. The flow state in the oxidizer zone is not addressed specifically. Separation of the sulfur particles takes place in a separate vessel.
U.S. Pat. No. 6,596,253 B1 discloses a process for desulfurization of a gaseous feed containing hydrogen sulfide. The sulfur particles and the reduced catalyst solution are separated in a preliminary step and the stream of reduced catalyst solution is sent to a downstream oxidizer.
General principles for use of ferric chelates for the oxidization of hydrogen sulfide are disclosed in lliuta I., et al., ‘Concept of bifunctional Redox iron-chelate process for H2S removal in pulp and paper atmospheric emissions’, Chemical Engineering Science, Oxford, GB, volume 58, no. 34-24, December 2003, pages 5305-5314.